Pulse-modulated wave-signal generator



May 3, 1949. J. J. OKRENT PULSE-MODULATED WAVE-SIGNAL GENERATOR FiledJune 6, 1945 FlG.l

FIG. 2

INVENTOR. JAsPERyKRENT Patented May 3, 1949 PULSE-MODULATED WAVE-SIGNALGENERATOR Jasper J. Okrent, Great Neck, N. Y., assignor, by mesneassignments, to Hazeltine Research, Inc., Chicago, Ill, a corporation ofIllinois Application June 6, 1945, Serial No. 597,777

9 Claims.

This invention relates, in general, to Wavesignal generators. It isespecially directed to arrangements in which wave signals of pulse Waveform having a predetermined duration are produced by controlling anoscillation generator having an operating frequency the period of whichis much less than the duration of the pulse signals to be produced.While the invention is subject to a variety of applications, it isparticularly suited to radio-locator and direction finder systemsutilizing pulse-modulated highfrequency signals and will be described indetail in that connection.

In certain radio-locator and direction-finder systems a pulse ofhigh-frequency energy having a desired duration is transmitted and areflection thereof, picked up by a suitable receiver, is used inobtaining the required direction-finding or locating information.Frequently, the transmitting and receiving units are interconnected sothat the transmitter is keyed into a succeeding cycle of operationfollowing the receipt at the receiver of a reflection of a giventransmitted pulse. in one such arrangement of the prior art, thetransmitter comprises a high-frequency oscillation generator whichincludes a vacuum tube having anode, cathode, and control elec trodesbut normally having no anode-cathode excitation potential. A keyed orsynchronized blocking oscillator is associated with the highfrequencygenerator for applying a pulse of eX- ci-tation potential to the anodeand cathode electrodes thereof. The applied pulse of potential initiatesoscillations in the high-frequency generator and sustains theseoscillations as required to produce an output pulse for transmission.Usually, the blocking oscillator is keyed in response to an outputsignal of the receiver unit to effect pulse-by-pulse operation. That is,an output pulse is transmitted in response to each received pulse Viewof the link or control extending from the receiver to the transmitter.

described arrangement is satisfactory for many installations but may notprovide sufficient control over the duration of the transmitted pulsesfor other installations. It is found that the starting time of thehigh-frequency oscillation generator in response to an'applied pulse ofexcitation potential may be variable. By starting time is meant theinterval between the application of the pulse of potential and theinitiatic-n. of cscil. ti It may vary with such factors a thecharact.,.1stics of the vacuum tube emp. ,d in. the high-frequencygenerator, the components associated therewith and the conditions ofloading. As a result, the transmitted pulses are shorter than theapplied pulse of excitation potential by the starting time and have anundesirably variable duration.

It is an object of the present invention, therefore, to provide animproved arrangement for generating wave signals of pulse wave form andwhich substantially avoids the aforementioned limitation of prior artarrangements.

It is a particular object of the invention to provide an improvedarrangement including an oscillation generator controlled by an appliedcontrol signal to produce wave signals of pulse wave form, each pulse ofwhich has a prede termined duration.

In accordance with the invention, an arrangement for generating wavesignals of pulse wave form comprises a Wave-signal oscillation generatorhaving output circuit and normally maintained in a nonconductingcondition. The arrangement has means for supplying to the oscillationgenerator a control pulse which is effective to initiate and sustainoscillations therein to produce a wave signal. There is also provided atimedelay system coupled to the output circuit of the generator to beresponsive to the initiation of the aforesaid oscillations for derivinga control poten tial and for utilizing the control potential effectivelyto interrupt the control pulse and restore the oscillation generator toits normal nonconducting condition a predetermined time intervalfoliowing the initiation of oscillations. The arrangement furtherincludes means for deriving from the oscillation generator an outputwave signal of pulse wave form, each pulse of which has a durationcorresponding to the above-mentioned predetermined time interval.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the following.description taken in connection with the accompanying drawing, and itsscope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a schematic representation of a Wave-signalgenerator embodying the. present invention; Fig. 2 comprises graphs usedin explaining the operation of the Fig. I arrangement; and Fig. 3represents schematically a. modification of a portion of the Fig. 1arrangement.

Referring now more particularly to Fig. 1, there represented anarrangement for generating wave signals of pulse wave form, specificallypulses or bursts of high-frequency energy having a desired predeterminedduration. The arrange- 3 ment comprises a high-frequency oscillationgenerator to be controlled, in a manner made clear hereinafter, toproduce output signals of pulse wave form, each pulse of which has adesired duration. This generator includes an electron-discharge deviceor triode vacuum tube I having an anode, a cathode, and a controlelectrode. A frequency-determining circuit, provided by an adjustableinductor I I and a condenser I2, is coupled by way of condensers I3 andI4 to the anode and control electrodes, respectively, of tube I0.Condenser I2 is shown in broken-line construction since it may becomprised, in whole or in part, of the distributed capacitance ofinductor II and stray capacitances associated therewith. The center tapof inductor I I is grounded as is the cathode of tube I0, thereby tocomplete the alternating current paths of the generator. A leak resistorI5 is connected to the control electrode of the tube. This tube isnormally maintained in a nonconductive condition since no excitationpotential is normally applied to its anode and cathode electrodes.However, oscillations may be initiated and sustained within the eneratorby applying a control signal or a pulse of excitation potential to tubeIt by way of a pulse transformer 20, the secondary winding of which isdirectly coupled between the anode and cathode electrodes of tube I0.Inductor 2l is a choke for signals having a frequency corresponding tothe operating frequency of the oscillation generator. Condenser 22 is aby-pass for such signals. The frequency-determining circuit of thedescribed oscillation generator is selected to provide an operatingfrequency the period of which is very much less than the desired pulseduration of the wave signals to be produced.

The arrangement of Fig. 1 has means for supplying to the high-frequencygenerator a control signal that is effective to initiate and sustainoscillations therein in order to produce an output wave signal. Thismeans comprises a relaxation oscillator, specifically a blockingoscillator, coupled to the high-frequency generator and including atriode vacuum tube 25. A source of space current, indicated +B, isconnected by way of a first winding 26a of a pulse transformer 26 to theanode of tube 25. A second winding 26b of transformer 26, connected withthe control electrode of tube 25 and inductively coupled with winding26a, provides a regenerative feedback between the input and the outputcircuits. A time-constant circuit consisting of a condenser 21 and aresistor 28 is also connected with the control electrode of tube 25 tocontrol the operating cycle of the blocking oscillator in well-knownmanner. Tube 25 is normally blocked by a holding voltage applied to itscontrol electrode from a source of bias potential, indicated --Ec.Preferably, the parameters of the blocking oscillator are so selectedthat the control pulse or signal generated in each uninterrupted cycleof operation has a duration which is longer than the desired pulseduration of the wave signals to be produced in high-frequency oscillatorIII.

A third winding 26a of pulse transformer 26 is coupled to the blockingoscillator for applying the output signal obtained therefrom to a pulseamplifier including the tetrode vacuum tube 30. The primary winding ofpulse transformer 20 is included in the output circuit of tube 30 andoperating potentials are applied to the tube from thesources indicated+B, +80 and -Ec. The source Ec has such a value that the pulse amplifieris normally maintained in a non-conductive condition. The windings ofpulse transformers 20 and 26 are so poled that the pulse output of theblocking oscillator is applied to the anode-cathode circuit of tube Illwith positive polarity.

A keying or synchronizing circuit is associated with the blockingoscillator for keying the oscillator into operation when a Wave signalof highfrequency energy is desired from high-frequency generator III.The synchronizing circuit comprises an input terminal 35 coupled througha condenser 36 to the input circuit of a triode vacuum tube repeater 31.The anode and cathode electrodes of tube 31 ar arranged in parallelrelationship with the corresponding elements of tube 25. Repeater 31 isnormally biased to anode current cutoff by way of a potential source,in- I dicated Ec, connected with the control electrode thereof through aresistor 38.

The pulse duration of the wave signal generated by high-frequencyoscillator I0 is controlled by a time-delay means responsive to theinitiation of oscillations therein for deriving a control potential andfor utilizing the control potential effectively to interrupt the controlsignal applied to tube I0 and restore the high-frequency oscillator toits normal nonconductive condition a predetermined time intervalfollowing the initiation of oscillations therein. This means comprises adiode 40 which is coupled with the frequencydetermining circuit ofhigh-frequency oscillator I 0 by way of an inductor 41, coupled withinductor II as indicated by the bracket M. The input terminals 41, 41 ofa time-delay network are connected through inductor 4| across theelectrodes of diode 40 for utilizing a control voltage derivedtherefrom. The delay network has a conventional construction includingseries-connected inductors 42, 42 and intervening shunt-connectedcondensers 43, 43. The output terminals 48, 48 of the time-delay networkare terminated in a resistor 44 selected to provide a terminationcorresponding to the characteristic impedance of the network. Resistor44 is included in the input circuit of a vacuum-tube repeater 45 whichis normally biased to anode current cutoff by a suitable sourceindicated Ec. A condenser 46 couples the output circuit of repeater 45to the input circuit of blocking oscillator 25.

An antenna-ground system 50, including an inductor 5| coupled with thefrequency-determining circuit of high-frequency oscillator I0,constitutes means for deriving therefrom an output wave signal of pulsewave form, each pulse of which has a desired predetermined duration.

The arrangement of Fig. 1 may be utilized as the transmitting unit of aradio-locator and direction-finding system of the type referred toabove. Input terminal 35 may indicate an input terminal of thetransmitting unit which may be connected with an output terminal of theassociated receiver unit so that the operation of the transmitter iscontrolled by the receiver output. However, since a completeunderstanding of the present invention may be obtained from theschematic diagram of Fig. 1, the remaining portions of the radio-locatorand direction-finding system have been omitted from the drawing.

In considering the operation of the described arrangement, reference ismade to the curves of Fig. 2 in which curve A represents a synchronizingsignal applied at the time h with positive polarity to input terminal35. The synchronizing signal is repeated by repeater 31 and translatedby way of transformer windings 26a and 26b to the input circuit ofblocking oscillator 25 where it also appears with positive polarity. Thesynchronizing pulse thus initiates a cycle of .operation of theblockingoscillator which, if permitted to continue uninterruptedly,produces the output pulse of curve C in well understood manner. Thispulse has a duration t1-t4 which exceeds the pulse duration of the wavesignal to be produced in high-frequency generator iii. However, theoperation of the blocking oscillator is interrupted, in a manner to bedescribed presently, so that its output signal is represented by curveD.

If the time of signal translation through the pulse amplifier 36 beneglected, the amplified pulseoutput of the blocking oscillator isapplied at the tie 51 to the anode and cathode electrodes of tube itwith positive polarity, as represented by curve E. At the time t2oscillations are initiated in high-frequency oscillator it, where theinterval iv-$2 reprez-xents the starting-time interval defined hereinbefore. The oscillations once initiated continue for the remainingduration of the applied pulse of excitation potential and produce therequired output wave signal of highefrequency energy. In view of thecoupling between inductor ll of high-frequency oscillator l9 andinductor ll, the generated oscillations are rectified so that there isapplied, substantially at the time t2, 9, control pulse of positivepolarity to the input terminals 1?, 4'! of the tine-delay network. Thiscontrol pulse is represented in curve F. It traverses the time-delaynetwork and arrives at the terminating resistor M at the time 253 asshown by curve G, where the interval tzts represents the delay of thenetwork. At the time is the control pulse or potential renders repeaterd5 conductive and appears in the output circuit thereof as a signalpulse of negative polarity. This signal pulse of negative polarity isadded into the input circuit of the blocking oscillator 25 to block orinterrupt the normal operation of the blockin oscillator at the time is.At this same time is, the output pulse of the blocking oscillator andthe input pulse of excitation potential supplied to high-frequencyoscillator iii are to; ninated. The high-frequency oscillator ill isthus restored to its normal nonconductive condition, terminatingoscillations therein. Therefore, it is apparant that the high-frequencyoscillator generates oscillations and produces an output wave signalduring the interval ifs-ta corresponding to the delay of network d2,Bil. The time delay of the net work is adjusted to provide the desiredpulse duration for the output wave signal obtained from high-frequencyoscillator iii and transmitted by antenna system In Fig. 3 there isrepresented a modification of that portion of the Fig. 1 arrangementenclosed within. the broken-line rectangle 52. It represents the vacuumtube and frequencydctern'iining circuit of the high-frequencyoscillation generator, the several elements thereof being designated bythe same reference charac ters as in Fig. 1. t also represents thecoupling between high-frequency oscillator l8 and the input terminalsill, ill of the time-delay network. Only the input terminals, the firstshuntconnected condenser 33 and the first inductor of the delay networkare shown. This circuit comprises a triode amplifier iiil which has aninput circuit coupled across resistor iii of the hi'ghdrequencygenerator and an output circuit coupled to the time-delay networkthrough a condenser 552. Tube bil is provided with a cathode impedance6! for developing a self-bias which maintains the tube in apredetermined conductive condition.

The operation of the wave-signal generator modified in the manner ofFig. 3 is generally similar to that of Fig. 1. In Fig. 3 advantage istaken of the fact that the high-frequency osci1- lation generator Illdevelops its own bias by grid current rectification. In view of thisfact, a voltage pulse of negative polarity is established acrossresistor it in the input circuits of tubes iii and kill almost as soonas the oscillations are initiated. This voltage pulse of negativepolarity is translated by vacuum tube till, appearing in output circuitthereof and at the input terminals ll, t"? of the time-delay networkwith positive polarity. The control potential traverses the time-delaynetwork, terminating the operation of blocking oscillator 25 andhigh-frequency oscillation generator ill, in the manner alreadydescribed, after a time interval which corresponds to the desired pulseduration of the wave signal to be transmitted.

In the illustrated embodiments of the invention, the control potentialderived in the output circuit repeater in response to the initiation ofoscillations in high-frequency generator I!) is applied directly to theblocking oscillator to interrupt its normal operation. It will beunderstood that this control potential may, if desired, be utilized toreduce the gain of pulse amplifier 39. In that case, the output circuitof repeater i5 is also to be connected to the control electrode of Thismay be accomplished by closing indicated in Fig. 1. By reducing the theswitches gain of this amplifier, the pulse of excitation potentialapplied to tube iii may be so reduced in tensity at the time interval isthat oscillations interrupted in high-frequency oscillator H) toterminate the generation of the output wave signal. Where this mode ofoperation is our pioyed, the control signal or pulse of excitationpotential applied from the blocking oscillator to the high-frequencyoscillation generator may be said to effectively interrupted.

In the preferred embodiments of the invention, the circuit of blockingoscillator 2-5 is so adjusted that its normal or uninterruptedconductive period, represented t1-"t4 in Fig. 2, is not very much longerthan the desired pulse duration of the Wave signals obtained inhigh-frequency generator Ell. Where this adjustment is made, the controlpotential applied to the blocking oscillator from repeater may have arelatively low intensity and yet be able to block the operation of tubeThis adjustment also prevents the generation of excessively long pulsesby the blockoscillator in the event of failure of tubes 38 or iii.

While there have been described what are at present considered to be thepreferred embodimerits of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. An arrangement for enerating wave sigof pulse wave form comprising, awave-signal oscillation generator having an output circuit and normallymaintained in a nonconducting condition, means for supplying to saidgenerator control pulse efiective to initiate and sustainos cillationstherein to produce a wave signal, a timedelay system coupledto saidoutput circuit of said generator to be responsive to the initiation ofsaid oscillations for deriving a control potential and for utilizingsaid control potential effectively to interrupt said control pulse andrestore said generator to its normal nonconducting condition apredetermined time interval following the initiation of saidoscillations, and means for deriving from said generator an output wavesignal of pulse wave form, each pulse of which has a durationcorresponding to said predetermined time interval.

2. An arrangement for generating wave signals of pulse wave formcomprising, a wave-signal oscillation generator having an output circuitand normally maintained in a nonconducting condition, means forsupplying to said generator a con trol pulse effective to initiate andsustain oscillations therein to produce a wave signal, a control systemcoupled to said output circuit of said generator to be responsive to theinitiation of said oscillations for deriving a control potential,timedelay means for utilizing said control potential effectively tointerrupt said control pulse and restore said generator to its normalnonconducting condition a predetermined time interval following theinitiation of said oscillations, and means for deriving from saidgenerator an output wave signal of pulse wave form, each pulse of whichhas a duration corresponding to said predetermined time interval.

3. An arrangement for generating wave signals comprising, a wave-signaloscillation generator having an output circuit and normally maintainedin a nonconducting condition, means for supplying to said generator acontrol pulse effective to initiate and sustain oscillations therein toproduce a wave signal, means coupled to said output circuit of saidgenerator and including a rectifier for rectifying said oscillations toderive a control potential and a time-delay network for utilizing saidcontrol potential effectively to interrupt said control pulse andrestore said generator to its normal nonconducting condition apredetermined time interval following the initiation of saidoscillations, and means for deriving from said generator an output wavesignal of pulse Wave form, each pulse of which has a durationcorresponding to said predetermined time in terval.

4. An arrangement for generating wave signals comprising, a wave-signaloscillation generator having an output circuit and normally maintainedin a nonconducting condition, means includin an auxiliary generator forsupplying to said oscillation generator a control pulse effective toinitiate and sustain oscillations therein to produce a Wave signal, atime-delay system coupled to said output circuit of said oscillationgenerator to be responsive to the initiation of said oscillations forderiving a control potential and for utilizing said control potentialefiectively to block said auxiliary generator and restore saidoscillation generator to its normal nonconducting condition apredetermined time interval following the initiation of saidoscillations, and means for deriving from said oscillation generator anoutput wave signal of pulse wave form, each pulse of which has aduration corresponding to said predetermined time interval.

5. An arrangement for generating Wave signals comprising, a wave-signaloscillation generator having an utput'circuit for producing an outputwave signal of pulse wave form having a predetermined pulse duration butnormally maintained in a nonconducting condition, a relaxationoscillator coupled to said oscillation generator for normally supplyingthereto a control pulse having a duration substantially exceeding saidpredetermined duration and effective to initiate and sustainoscillations in said oscillation generator to produce said output wavesignal, a time-delay system coupled to said output circuit of saidoscillation generator to be responsive to the initiation of saidoscillations for deriving a control potential and for utilizing saidcontrol potential effectively to block said relaxation oscillator andrestore said oscillation generator to its normal nonconducting conditionat a time interval following the initiation of said oscillations equalto said predetermined pulse duration, and means for deriving said outputwave signal from said oscillation generator.

6. An arrangement for generating wave signals comprising, a wave-signaloscillation generator having an output circuit for producing an outputwave signal of pulse wave form having a predetermined pulse duration butnormally maintained in a nonconducting condition, a blocking Ioscillator coupled to said oscillation generator for normally supplyingthereto a control pulse having a duration substantially exceeding saidpredetermined duration and effective to initiate and sustainoscillations to said oscillation generator to produce said output wavesignal, a timedelay system coupled to said output circuit of saidgenerator to be responsive to the initiation of said oscillations forderiving a control potential and for utilizing said control potentialeffectively to block said blocking oscillator and restore saidoscillation generator to its normal nonconducting condition at a timeinterval following the initiation of said oscillations equal to saidpredetermined pulse duration, and means for deriving said output wavesignal from said oscillation generator.

7. An arrangement for generating wave signals comprising, a wave-signaloscillation generator having an output circuit and including anelectron-discharge device having an anode and a cathode for producing anoutput wave signal of pulse wave form having a predetermined pulseduration but normally maintained in a nonconducting condition, arelaxation oscillator for normally applying between said anode andcathode a pulse of excitation potential having a duration substantiallyexceeding said predetermined duration and efiective to initiate andsustain oscillations in said oscillation generator to produce saidoutput wave signal, a time-delay system coupled to said output circuitof said generator to be responsive to the initiation of saidoscillations for deriving a control potential and for utilizing saidcontrol potential effectively to block said relaxation oscillator andrestore said oscillation generator to its normal nonconducting conditionat a time interval following the initiation of said oscillations equalto said predetermined pulse duration, andmeans for deriving said outputWave signal from said oscillation generator.

8. An arrangement for generating wave signals comprising, a wave-signaloscillation generator including an electron-discharge device having ananode, a cathode, and a control electrode but normally maintained in anonconducting condition, means for supplying to said generator a controlpulse effective to initiate and sustain oscillations therein to producea wave signal, time-delay means coupled between saidcathode and controlelectrode and responsive to the initiation of said oscillations forderiving a control potential and for utilizing said control potentialefiectively to interrupt said control pulse and restore said generatorto its normal nonconducting condition a predetermined time intervalfollowing the initiation of said oscillations, and means for derivingfrom said generator an output wave signal of pulse wave form, each pulseof which has a duration corresponding to said predetermined timeinterval.

9. An arrangement for generating Wave signals of pulse Wave formcomprising, a wave-signal oscillation generator having an output circuitand having an operating frequency the period of which is very much lessthan the pulse duration of the wave signals to be generated but normallymaintained in a nonconducting condition, means for supplying to saidgenerator a control pulse effective to initiate and sustain oscillationstherein to produce a wave signal, a time-delay system coupled to saidoutput circuit of said generator to be responsive to the initiation ofsaid REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS Number Name Date 2,089,781 Buschbeck Aug. 10, 19372,137,351 Schlesinger Nov. 22, 1938 2,333,688 Shepard Nov. 9, 19432,413,182 Hollingsworth et al. Dec. 24, 1946

